Multiple disk brake system with integrated parking brake

ABSTRACT

A brake system ( 10 ) comprises a disc brake ( 30 ) and a drum brake ( 50 ), and a hub ( 20 ). The hub ( 20 ) comprises a mounting portion ( 20   a ) generally having the shape of a hollow cylinder. The disc brake ( 30 ) comprises a disc ( 32 ) mounted on our outer surface of said portion ( 20   c ) of the hub for rotation with the hub, the disc ( 32 ) also being mounted for axial sliding movement on the hub ( 20 ). The drum brake ( 50 ) comprises frictional material shoes ( 56 ) which are moveable into engagement with an internal cylindrical surface ( 20   e ) of said mounting portion ( 20   c ) of the hub ( 20 ) to act as a parking brake.

This invention is concerned with a brake system eg for a vehicle.

Many vehicles are equipped with disc brakes to fulfil the primarybraking function of stopping or slowing the vehicle. Such disc brakesare often operated by a foot pedal and hence do not operate in theabsence of the driver. For this reason, the vehicles are equipped with aparking brake which can be held in a “brakes on” condition in theabsence of the driver, the parking brake serving to prevent the vehiclefrom moving from rest. Conventionally, such parking brakes are of thedrum brake type, comprising a hollow cylindrical drum and two “shoes”comprising friction material. The shoes are mechanically-operated toengage the inner cylindrical surface of the drum with a braking force.Thus, the overall brake system has a considerable weight.

It is common for the disc of a disc brake to be the so-called “top-hat”type comprising an annular inner portion which is bolted to a hub, ajoining portion which is generally cylindrical and extends axially ofthe hub, and an annular friction material-engaging portion joined to theinner portion by the joining portion. In order to save weight, theinterior surface of the joining portion is often utilised as the drum ofa drum type parking brake, thereby eliminating the necessity for aseparate drum. However, where the disc is not of the top-hat type, thissolution is not available.

GB 2031538 A, in connection with FIG. 4 thereof, discloses a brake ofthe enclosed type suitable for use in the agricultural or constructionindustries. This brake has a hollow cylindrical hub portion ofrelatively small diameter which provides a mounting for a disc of a discbrake. Axially spaced from but integral with said hub portion is afurther hollow cylindrical hub portion of much greater diameter whichserves as the drum of a drum parking brake. Thus, the disc mounting andthe drum are provided by different portions of the hub.

In WO 98/25804, a disc brake is described in which at least one disc ismounted on a hub. The disc is mounted on the hub by means of mountingmeans arranged so that the hub and the disc rotate about the centralaxis of the hub as a unit but the disc can perform axial slidingmovement on the hub. The specific example given in WO 98/25804 has twodiscs mounted on the same hub, both being slidable axially. The brakealso comprises a piston and cylinder assembly having its cylinder fixedrelative to a suspension link of a vehicle, the cylinder beingintegrally formed with the link. The system also comprises a caliperfixed relative to the cylinder, the caliper providing supports forfriction pads of the system, including pads between the two discs. Thepad furthest from the assembly is fixed to the caliper but the remainingpads are slidably mounted thereon. When the piston and cylinder assemblyis operated, the pad operated upon by the assembly and the pads betweenthe discs slide on the caliper, and the discs slide on the hub untileach disc is engaged on both sides by a pad.

The disc brake of WO 98/25804 operates on a hub which comprises amounting portion on which the discs are mounted. The mounting portion isgenerally in the shape of a hollow cylinder, the discs being mounted onthe outer cylindrical surface thereof. The disc brake is for a drivenhub and the interior of the mounting portion is occupied by a connectionbetween the hub and a drive shaft.

It is an object of the present invention to provide a brake system ofthe general type disclosed in WO 98/25804, the system being of reducedweight.

The invention provides a brake system comprising a disc brake, a drumbrake, and a hub arranged to rotate about a central axis thereof, thehub comprising a mounting portion generally having the shape of a hollowcylinder centred on said axis, the disc brake comprising a disc mountedon an outer surface of said mounting portion of the hub for rotationwith the hub, the disc also being mounted for axial sliding movement onthe hub, characterised in that the drum brake comprises frictionmaterial shoes which are moveable into engagement with an internalcylindrical surface of said mounting portion of the hub to act as aparking brake.

In a brake system according to the invention, the same hollowcylindrical portion of the hub is utilised both as the mounting portionof the disc of a disc brake and also as the drum of a drum brake,thereby avoiding the necessity for a separate drum or drum portion,giving a lighter, simpler and more compact brake.

There now follows a detailed description, to be read with reference tothe accompanying drawings, of a brake system which is illustrative ofthe invention.

IN THE DRAWINGS

FIG. 1 is a vertical cross-sectional view taken through the illustrativebrake system;

FIG. 2 is a view of a portion of the illustrative brake system taken inthe direction of the arrow II in FIG. 1; and

FIG. 3 is a view of a further portion of the illustrative brake systemtaken in the direction of the arrow III in FIG. 1.

The illustrative brake system 10 shown in the drawings is mounted on asuspension link 12 of a vehicle. On one side thereof, the link 12 has anupper vertical mounting surface 12 a and a lower vertical mountingsurface 12 b (see FIG. 1). A cylindrical recess 14 is formed in the link12 and has an opening through the surface 12 a. The recess 14 has aconnection between its bottom surface and a connecting point 16 in thelink 12 for a hydraulic pipe (not shown) so that hydraulic fluid underpressure can be delivered to the recess 14 so that (as further describedbelow) the recess 14 can be utilised as the cylinder of ahydraulically-operated piston and cylinder assembly of a disc brake ofthe system 10. The link 12 also supports a stub axle 18 which extendshorizontally from the lower mounting surface 12 b.

The illustrative brake system 10 also comprises a hub 20 which ismounted on the stub axle 18 on bearings 22. The hub 20 is mounted forrotation about a central horizontal axis 24 thereof. The hub 20comprises a central portion 20 a which houses the bearings 22, anannular flange portion 20 b which extends vertically at one end of theportion 20 a, and a mounting portion 20 c generally having the shape ofa hollow cylinder centred on the axis 24. The flange portion 20 bprovides an annular vertical mounting surface 20 d to which a wheel (notshown) can be bolted by bolts 26 in a conventional manner. The mountingportion 20 c is joined to an outer peripheral portion of the flangeportion 20 b and extends around the central portion 20 a.

The illustrative brake system 10 also comprises a disc brake 30 which isgenerally of the type disclosed in WO 98/25804. The brake 30 comprisestwo discs 32 which are in the form of annular plates formed of steel.The discs 32 are mounted on the outer surface of mounting portion 20 cof the hub 20 so that the discs 32 rotate with the hub 20 about the axis24 and so that the discs 32 can perform axial sliding movement on thehub 20. Specifically, grooves 34 are formed in the external surface ofthe mounting portion 20 c, each groove 34 extending parallel to the axis24, and teeth 36 project from the discs 32 into the grooves 34. Theteeth 36 serve to transmit rotational forces between the discs 32 andthe hub 20 and can slide axially along the grooves 34. As disclosed inWO 98/25804, leaf springs (not shown) provide resilient means actingbetween the hub 20 and the discs 32 to apply radial force to control themovement of the discs 32.

The disc brake 30 also comprises friction material pads 38 which aremounted on both sides of each of the discs 32. There are four pads 38,these being an outer pad 38 which is mounted on an abutment 39 which isfixed relative to the link 12, two central pads 38 which are between thediscs 32 and are mounted for axial movement, and an inner pad 38(closest to the link 12) which is also mounted for axial movement.Specifically, a caliper 40 is secured to the mounting surface 12 a ofthe link 12 by two bolts 42. The abutment 39 is secured to the caliper40 by the bolts 42 and the central and inner pads 38 are mounted onsupports 44 which are slidable on the outside surfaces of the caliper40, the central pads 38 being mounted on opposite surfaces of the samesupport 44. Specifically, the supports 44 have hook-like projections 44a (see FIG. 2) which hook over side surfaces of the caliper 40 which,thus, provides a slideway extending axially.

The disc brake 30 also comprises an operating mechanism operable tobring the pads 38 into contact with the opposite surfaces of the discs32 so that braking force is applied to the discs 32. The operatingmechanism is provided by the aforementioned piston and cylinder assemblywhich comprises a piston 46 mounted in the recess 14 of the link 12, therecess 14 providing the cylinder of the assembly. The assembly alsocomprises a sealing ring 48 mounted in a groove in the wall of therecess 14 and engaging the outer surface of the piston 46. Whenhydraulic fluid under pressure is applied to the connection point 16,the piston 46 is urged out of the recess 14. The piston 46 engages thesupport 44 of the inner pad 38 and moves it along the caliper 40. Theinner pad 38 then engages one of the discs 32 causing it to slide on thehub 20. This disc 32 then engages one of the central pads 38, causingthe support 44 of both central pads 38 to move along the caliper 40. Theother central pad 38 then engages the other disc 32 and moves it on thehub 20. This disc 32 then engages the fixed outer pad 38 when each disc32 is engaged on both sides by a pad 38.

The illustrative brake system 10 also comprises a drum brake 50 arrangedto serve as a parking brake to prevent rotation of the hub 20 when thebrake 50 is applied. The drum brake 50 comprises a supporting plate 52which is bolted to the mounting surface 12 b of the link 12 by bolts 54,the plate 52 having a central hole through which the stub axle 18passes. The drum brake 50 is positioned in the space between the portion20 a of the hub 20 and the internal cylindrical surface 20 e of themounting portion 20 c of the hub 20. The drum brake 50 comprises twofriction material shoes 56 which are arcuate having convex surfaceswhich face the surface 20 e of the mounting portion 20 c. The shoes 56are mounted on arcuate supports 58 which are pivotal at one end thereofon a horizontal pin 60 supported by the plate 52. The other end of eachof the supports 58 engages a cam 62 which is arranged to be turned abouta horizontal pin 64 by operation of a lever 66. The pin 64 is supportedby the plate 52 and the lever 66 projects through a space between theplate 52 and the mounting portion 20 c of the hub 20. The supports 58are arranged so that they leave sufficient space between them for theportion 20 a of the hub 20. The cam 62 has a shorter radial extent whichengages the supports 58 when the drum brake 50 is in an inoperativecondition but, by operation of the lever 66, can be turned into anoperative condition in which a larger radial extent of the cam 62engages the supports 58. A spring 68 acts between the supports 58 tokeep them in contact with the cam 62. In moving from the inoperativecondition to the operative condition thereof, the cam 62 pivots thesupports 58 about the pin 60, thereby moving the shoes 56 apart and intoengagement with the surface 20 e of the mounting portion 20 c of the hub20 so that the drum brake 50 acts as a parking brake.

What is claimed is:
 1. A brake disc system comprising a disc brake, adrum brake, and a hub arranged to rotate about a central axis thereof,the hub comprising a mounting portion generally having the shape of ahollow cylinder centred on said axis, the disk brake comprising a discmounted on an outer surface of said mounting portion of the hub forrotation with the hub, the disc also being mounted for axial slidingmovement on the hub, wherein the drum brake comprises friction materialshoes which are moveable into engagement with an internal cylindricalsurface of said mounting portion of the hub to act as a parking brake,wherein the disc brake comprises an operating mechanism operable tocause friction material pads of the brake to engage both sides of saiddisc, the operating mechanism comprising a piston and cylinder assembly,the cylinder of which is formed integrally with a suspension link onwhich the hub is mounted.
 2. A brake system according to claim 1,characterised in that said disc brake comprises two discs mounted on thesame hub for rotation with the hub and for axial sliding movement onsaid hub.
 3. A brake system according to claim 1, wherein the drum brakecomprises two shoes of friction material pivotally mounted within themounting portion of the hub.
 4. A brake disc system according to claim1, wherein said disc and said friction material shoes are arranged inradially opposed relation to one another on opposite sides of the hub.